Digital maps are now finding their way to the public. We see them at many sites at Internet, in PC atlases, in handheld navigators, for instance of the GPS type, and in many other devices. Most data is geographically related and can therefore be presented at a map.
Digital map data is either in raster or vector form. Raster maps are easy to use in applications since they have a uniform data structure where each pixel represents a color or a natural feature class but they have many disadvantages compared to vector maps. The most obvious one is that they do not scale well since images turn blocky when zoomed. They also cannot contain extra information on features in the image. Vector maps on the other hand are more complex to use but offer more flexibility and contain more information.
Geographic databases can be very large and slow to access. Many geographic databases take several gigabyte of storage. Because of their complexity and size these databases are not used to the extent that they may deserve.
Preparation of data for a map application is a costly process. The most common technique today is to prepare one database for each presentation scale that the application uses. This makes it possible to see an overview of a large area without reading most of the database. The downside is of course that it is expensive and complex to handle several databases instead of one. Ideally one database would be efficient enough for the whole scale range that the application uses.